China Tells Some Plane Passengers to Keep Window Shades Closed for National Security

China’s Ministry of State Security has warned passengers against opening window shades during take-off and landing at airports used by both civil and military aviation, a move that runs counter to prevailing practices regarding aviation safety.

The warning, issued on WeChat Monday, was aimed at limiting the leak of sensitive military information through photos and videos taken by passengers during take-off or landing at dual-use airports, the South China Morning Post reported.

Read More: U.S. Hawks Must Finally Get Real About China

The ministry said in its post that passengers using dual-use facilities—almost a third of China’s airports—are prohibited from capturing images or videos of sensitive areas. It cited a recent incident in which a foreign national was suspected to have “illegally” captured images from the window of their plane.

Another flight was ordered to return to the gate for security checks after a passenger “repeatedly” opened his window shade during take-off to take photos. The passenger was then detained for seven days, the ministry said.

Passengers around the world are often asked to have their window shades up during take-off and landing for safety reasons, including to aid with evacuation in the case of emergency and for rescuers to be able to spot smoke and fire, according to Amsterdam’s Schipol Airport. However, the rules vary by airline and are not legal requirements.